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23 Geos Applications
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EXPAND.THD
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#: 18637 S13/GEOS Connection I
12-Mar-89 12:49:32
Sb: #Expanding C64 Memory
Fm: Ross Nash 72627,3536
To: [F] Ed Flinn/Sysop 76703,4032 (X)
I have a question about the 1764(?) memory expansion for the C64. I have not
looked into a memory expander for the C64 because it was my understanding that
the C64 could not expand its memory. Added memory could only be used as a
ramdisk. Is this true with 1764, or is it a real, contiguous memory expansion.
If it is not contiguous, how does it help GEOS run more efficently when there
are two different models of drives?
#: 18639 S13/GEOS Connection I
12-Mar-89 13:17:11
Sb: #18637-Expanding C64 Memory
Fm: Ed Flinn/Sysop 76703,4032
To: Ross Nash 72627,3536
Russ,
You're absolutely right, the 1764 does not really act as additional memory
for the 64, but as a *very* fast data storage device. When you're using a 1764
with GEOS 64, GEOS does a number of things to help itself. First, it enables
DMA for "MoveData" operations. I don't really understand that, the book says
it allows GEOS to move large amounts of data within the REU, and I know you can
see the improvement when you scan across a geoPaint file, for instance.
The next good thing it does is to store some information to make it quicker
to reboot back to GEOS after exiting to BASIC.
It's when we get to disks that life gets really fun. The 1764 can be used
as though it were a disk drive. This isn't the RAMDOS programs, but is built
into GEOS, activated from the Configure program. You have two choices as to
how to do it. The first is easy to understand, and is called 'RAM 1541'. It's
just a RAMdisk, the size of a 1541. It's blindingly fast, and supports all
GEOS operations. You do, of course, have to remember to copy what you want
there each time you boot GEOS, and especially remember to copy anything you
want to save off of it before you power down the computer.
The other choice may be even more useful, if you have two real drives
already. The 1764 can be used to "shadow" a real 1541. The concept of
shadowing is:
As GEOS requests that a particular sector on the disk be read, a table in
the REU is checked. If that sector has not already been read, then it is read,
passed to GEOS, and also placed in the RAM "sector" in the REU. The next time
GEOS calls for that sector, the table look-up will find it in the REU, and it
will be passed to GEOS from there, with no disk I/O occurring. All writes go to
the REU and the disk immediately. The greatest way to demonstate this for
yourself is to place a geoPaint file on a shadowed disk. Open it and scroll
down it. It'll be as slow as usual. Now scroll back up. Since all the sectors
are now being read from REU instead of 1541, there's no delay. Fast!
I hope I've explained this well, sometimes I get carried away <grin>
#: 18720 S13/GEOS Connection I
16-Mar-89 15:17:50
Sb: #18637-Expanding C64 Memory
Fm: Anthony Marsh 72127,2301
To: Ross Nash 72627,3536
As usual Ed gave a very good explanation. Some further info: The Commodore 64
uses a 6502 CPU chip so it can only see 64K at one time. Same problem for the
128 and other computers. So what the 128 and others do is have banks of 64K and
flip back and forth between them. Some hardware hackers have been doing a
similar thing for the 64. There was an article in a recent Transactor I think
giving directions on how to do that. But the nice thing about the REU is that
the DMA is much faster than reading in bytes. It can flip between looking at
one range of bytes in one bank to another almost instantaneously. So if you can
find one, please buy it. Also if you use GEOS 2.0, you can not use two
different types of disk drives to maximum potential and it is too slow, so the
REU is almost a necessity. The biggest problem now is interfacing the REU into
our favorite programs. Almost impossible with commercial programs that don't
make special provisions for it. There are some nice programs that do use it,
but not enough. I got mine for $55 on a closeout at Service Mechandise and keep
your eyes out for people selling them when they go for an AMIGA. Tony